This invention relates broadly to wheels of the type which employ multipiece rims to facilitate tire mounting and demounting in a manner well known to those involved with the manufacture, use and maintenance of large-diameter wheels for earthmovers, loaders, mine haulage trucks, farm tractors and other off-road vehicles. The standard structural components of such rims and their functions are well understood and need not be described in detail; however, to illustrate the general nature of the present invention, it should be indicated that such rims typically include: a cylindrical rim base, a conical bead seat band, a flared flange ring at each end of the base, an O-ring gasket and a lock ring of the split type. The bead seat band slides axially over the gutter end of the base and has a radially upstanding end wall which abuts with an adjacent flange ring. When the rim parts are assembled, the lock ring is partially recessed radially in a groove formed about the gutter end of the base; and, a beveled side wall of the lock ring is engaged by a reversely sloped surface of the bead seat band. As the tire is pressurized, the flange which engages the bead seat band presses the latter axially against the lock ring causing the ring to wedge axially outwardly and radially inwardly with respect to its receptive groove in the base. So long as inflationary pressure acts upon the flange, bead seat band and lock ring with sufficient force, frictional engagement with the intermediate lock ring will alone provide a non-slip driving interconnection between the base and bead seat band.
As the size of many vehicles and their load capacities have grown, torques acting on the wheel rim and the rubber tires mounted thereon have increased proportionately. In fact, so great are the driving and breaking torques encountered in the normal operation of many contemporary large-wheeled vehicles that angular slippage almost always occurs between the bead seat band and the rim unless the aforedescribed frictional engagement between various rim parts is augmented by positive, structural interengagement of these parts. The problems caused by bead seat band slippage relative to the rim base are fully appreciated by equipment owners, operators and maintenance personnel; and, principal among these problems are degradation of equipment performance, severe tire distortion resulting in the rapid destruction of the tire beads and walls, and, in tubeless tire applications, complete failure of the O-ring air sealing gasket captured between the rim and the bead seat band. Should an O-ring gasket be destroyed or displaced, tubeless tires will quickly deflate leading to possible damage or destruction of the tire and, perhaps, the rim as well. Substantial expenses are always encountered in servicing and repairing the tires and rims of large vehicles, particularly in the field or underground; and, costly equipment down time and lost time for operating personnel can be expected.
Many inventions intended to remedy some of the aforenoted problems arising from rim to bead seat band slippage have been devised; and, several have been patented in this country. One type of device employed for structurally interconnecting the bead seat band to the ring is disclosed in early U.S. Pat. No. 3,003,533 issued to Gerbeth wherein a cross-shaped torque transmitting driving key has one projecting arm inserted in a pocket defined by a C-shaped lug welded to the periphery of the base at its gutter end; and, such key has another oppositely projecting arm loosely captured in an axially notched member welded to the upstanding peripheral wall of the bead seat band. U.S. Pat. No. 3,599,697 issued to Gerbeth and U.S. Pat. No. 5,107,914 issued to Yamoto et al disclose useful changes in the configuration of certain driver components intended to reduce welding-induced stress concentrations in the bead seat band and to close certain clearances between interfitting parts of Gerbeth's loose key driver. Not withstanding the continued popularity of the Gerbeth '538 driver, notable problems remain, namely:
The axially projecting pocket members and coacting loose key are extremely vulnerable to accidental impacting and damage on the job. PA1 The substantial clearances between parts originally intended to render the Gerbeth type driver easy to assemble and disassemble, in fact, invite the entrance of cement-like detritus and corrosion which may so adhere the parts that they must be destructively removed and thereafter replaced each time the rim parts are disassembled. PA1 The loose tolerances designed into the '538 pocket-key device allows the key to cock and thereafter to produce localized areas of line driving contact whereby the driver components suffer early and rapid wearing leading to such structural and operational debilitation of the driver that deleterious slippage between the rim and the bead seat band can occur even if the driver key remains in place. PA1 Firstly, the driving connection between the lock ring and the rim base is accomplished without slotting or otherwise structurally degrading either the rim base or the lock ring. Instead, a stop key is fixed in the lock ring groove by welding or otherwise and projects radially outwardly intermediate the spaced ends of a split lock ring to prevent slippage of the lock ring after one or the other of its end surfaces abuts the stop key. PA1 Secondly, the driving connection between the lock ring and the bead seat band includes cams welded to the outboard surface of the lock ring proximate each each side of the gap therein. PA1 Although the normally narrow gap in the lock ring could be greatly enlarged for the sole purpose of providing space for a larger, stronger stop key, this modification alone would create a substantial risk that, under inflationary pressure, an exposed O-ring segment of accordingly greater arcuate length would be extruded outwardly through such an oversized gap. PA1 Use of the lock ring gap to receive the stop key in accordance with the Verdier patent also dictates that the lock ring have discrete load-bearing lugs or the like welded thereto on both sides of the gap for engaging and driving the bead seat band in opposed directions. Such weldments create modified lock ring segments having increased thickness and undesirable stiffness, as well as heat affected sections which are likely to exhibit localized degradation of desirable metallurgical properties established by careful selection of alloyed material and by previous heat treatment. PA1 Since the arcuate length of the separable driver block may be increased as required to fit any selectably lengthened gap in the lock ring, a keyway cut in the block can be beneficially lengthened to accept a longer key whereby a weldment of increased size and strength can be utilized to provide a more secure attachment of the key with the lock ring groove. PA1 Even where a wide lock ring gap is provided to afford a wider keyway and strengthened attachment of the key to the base, the O-ring will not extrude axially through the gap, as is the case with Verdier, because the gap is completely occupied by the block. Conversely, a correspondingly more substantial arcuate portion of the O-ring would be exposed should the driver block be inadvertently omitted during assembly of the rim. Thereafter, should a serviceman attempt to inflate a tire mounted on a rim with the driver block missing, the O-ring will push out harmlessly through the gap before substantial tire pressurization can occur. PA1 Because the crown of the driver block can be provided with a complementary set of cams required to coact with the cams carried by the bead seat band, the preselected strength and stiffness characteristics of the lock ring need not be degraded by welding cam blocks to the lock ring in the manner disclosed in the Verdier patent. PA1 both driver blocks can be produced by casting or forging and require only a minimum of additional operations to provide a required keyway and various load bearing surfaces. Moreover, the metallurigical specifications of the blocks need not be the same as those of the lock ring; therefore, the blocks can usually be made of less costly material and do not require additional heat treatment. PA1 Since the driver block comprises a rugged, one-piece member whose outboard surface registers with that of the lock ring, no part of the driver structure protrudes axially beyond the lock ring or the rim thereby greatly reducing the risks of damaging the driver on the job. However, should the driver block be damaged during operation of a vehicle or during assembly or disassembly of the lock ring, it can be more cheaply replaced than a lock ring having driver components welded thereto. PA1 Because the driver block is inserted in line with the confronting ends of the lock ring, there are no substantial spaces between these parts which would allow muck, rocks and other detritus to enter. PA1 The projecting crowned midsection of the block has an important secondary function beyond providing a pair of oppositely facing cam surfaces, namely, the additional material in the midsection compensates for any loss of strength and mass in the driver block where material is removed to form a keyway. PA1 Inasmuch as the present driver constructions serve to connect the rim base to the bead seat band yet do not require the lock ring itself to transmit more than its usual share of driving or braking torque, these drivers function without subjecting the lock ring to forces tending to stress the lock ring and to shift it in its groove with attendant wearing.
U.S. Pat. No. 3,106,237 to Holmes, U.S. Pat. No. 3,224,484 to Smith and U.S. Pat. No. 4,144,922 to Strader suggest that the lock ring be utilized to help alleviate the aforenoted problems created by the use of Gerbeth's loose key as a bead seat band driver. To this end, Holmes rabbets the split ends of his lock ring to receive and retain a loose key axially and radially in angularly aligned slots in the rim and in a flange ring fixed to the bead seat band, whereby the rim and flange ring are interlocked. Smith welds an axially projecting, T-shaped key to the axial outboard side of his lock ring. One arm of Smith's key interfits with a slot in the extreme axial end face of the rim and the other key arm interfits in a slotted lug welded to the outboard end of the bead seat band. Strader welds a pair of angularly spaced lugs to his lock ring and a T-shaped key is welded to the upright surface of a flange fixed to his bead seat band. Upon tire inflation, these lugs are interfittably received in angularly aligned slots in the outboard end of the rim; and, the upright leg of the T-shaped key is captured between the confronting lock ring surfaces defining the split or gap therein. In this fashion, the lugs, the lock ring and the T-shaped key provide an interconnected driving structure between Strader's rim and bead seat band.
In comparison with the previously discussed Gerbeth '538 loose key driver, Holmes, Smith and Strader reduce troublesome axial projection of driver components thereby protecting driver components from inadvertent battering and breaking. Furthermore, closer driving fits between the lock ring of each of the three drivers just discussed and the various lugs and key connecting these lock rings to their rims or to their bead seat bands provide superior angular alignment and less play between parts thereby reducing wearing of rim components. However, each of these structures requires that the extreme axial end of the rim be notched or otherwise cut away to receive some sort of lug projecting radially from the lock ring. Because such a notch comprises a structural discontinuity which localizes torque induced stresses in the notched area, cracks in the hub can occur through the notch. Even if a hub crack is minute, inflationary air will escape through the rim and troublesome and costly tire deflation will eventually result. In accordance with industry practice, inclusion of a notched base in a wheel assembly dictates a reduced maximum air pressure rating for such assembly. It will be noted that Strader has welded two lugs to his lock ring and has notched his rim at two angularly spaced points in order to divide shear forces on the order of 8000 pounds per square inch that are commonly generated by the wheel driving torque applied to the lock ring of large diameter rims. However, such plural notches in the rim base are apt to increase proportionally the risk of stress concentrations leading to rim failure. Not only must Holmes notch his rim as do Smith and Strader, but Holmes is required to cut notches in his flange ring and in his lock ring in order to connect all three of these parts by means of his loose key.
U.S. Pat. No. 3,459,252 issued to Verdier describes a driver for a bead seat band which is structurally distinguishable from the abovedescribed prior art drivers in these two significant regards:
It is evident that by placing a stop key in the lock ring groove, Verdier has provided a simple device for positively driving his lock ring which is not exposed to accidental battering, as in the Gerbeth driver, and which does not require notching the rim base, as do all of the Holmes, Smith and Strader drivers. However, Verdier's requirement that the stop key be sized for acceptance in the usual narrow gap in a lock ring creates the following inherent shortcomings for this class of driver: